Conventional cooling apparatuses of this type include the one disclosed in Japanese Laid-Open Patent Publication No. 2005-16433. The apparatus of the publication cools a vehicle engine by circulating coolant in a cooling circuit through the operation of a pump. The pump, which circulates coolant in the cooling circuit, may be a mechanical pump driven by the engine or an electric pump driven by a motor, which is a driving source separate from the engine.
When changing coolant in a cooling apparatus, old coolant is first drained from the circuit. Then, the circuit is filled with new coolant. After the filling of the new coolant, a certain amount of air remains in the cooling circuit. If the cooling circuit is started with the remaining air, the cooling efficiency of the engine and the discharge efficiency of the pump are lowered. Thus, an air bleeding portion needs to be provided to the cooling circuit, and air in the circuit needs to be caused to flow to the air bleeding portion, so that the air is discharged to the outside. In other words, air bleeding needs to be performed.
Specifically, such air bleeding is performed by causing air to the air bleeding portion by means of the flow of coolant in the cooling circuit using a pump when air exists in the cooling circuit, for example, after a change of the coolant. By causing the air in the cooling circuit to the air bleeding portion, the air is collected and stored in the air bleeding portion. This allows air in the cooling circuit to be discharged from the circuit.
By causing air in the cooling circuit to flow to the air bleeding portion through the operation of the pump, and storing the air in the air bleeding portion as described above, the air can be discharged from the cooling circuit. However, air in the cooling circuit cannot always be efficiently collected in the air bleeding portion, and it takes some time to collect the air in the air bleeding portion. This drawback is related to the fact that air exists in a number of sections in the cooling circuit, and the resistance to air flow differs from one section to another.
That is, if the coolant displacement of the pump for air bleeding is determined in accordance with the air located in sections of low resistance to air flow among several sections at which stagnant air exists in the cooling circuit, stagnant air in sections of high resistance to air flow cannot be caused to smoothly flow to the air bleeding portion by the flow of the coolant generated by the operation of the pump in the coolant circuit. Therefore, it requires some time to collect air in the cooling circuit to the air bleeding portion through the operation of the pump.
If the coolant displacement of the pump for air bleeding is determined in accordance with the air located in sections of high resistance to air flow in the cooling circuit, the flow of coolant generated by the operation of the pump is excessively strong for causing stagnant air in sections of low resistance to air flow to flow. As a result, such air is diffused in the coolant as bubbles. Thus, collecting air in the cooling circuit to the air bleeding portion through the operation of the pump takes relatively long time.
Such a problem is not uniquely found in a cooling apparatus that cools a vehicle engine, which is a subject of cooling and a heat source, but also substantially similarly found in any cooling apparatus that cools a subject of cooling other than vehicle engines.